This invention relates generally to machine tools having rotatable, toolholding spindles, and more specifically, to a spindle keylock for stopping and locking the spindle of a machine tool at a predetermined angular orientation with respect to a fixed plane passing through the spindle axis.
In the operation of horizontal spindle and vertical spindle machine tools, particularly those having automatic tool changers thereon, it is usually necessary to stop and lock the machine tool spindle at a predetermined angular position so that the machine tool spindle key is aligned with the toolholder key. Unless the toolholder key is aligned with the spindle key, the toolholder will not firmly engage the spindle, thereby preventing complete transmission of torque from the spindle to the toolholder.
Heretofore, various devices have been proposed to stop and lock the spindle of a machine tool at a predetermined angular orientation to assure alignment of the toolholder key with the spindle key. Sedgwick et al in U.S. Pat. No. 3,704,510 issued on Dec. 5, 1972 discloses a servo control system which utilizes a position synchro to control spindle drive motor excitation so that spindle rotation ceases and a braking force is applied to the spindle to locate the spindle at a predetermined angular orientation, thereby assuring that the spindle key aligns with a complementary toolholder key. A somewhat different servo control system is described in U.S. Pat. No. 3,874,071 issued Apr. 1, 1975 to Kato. A pair of synchro generators, one for measuring the angular toolholder position and the other for measuring the angular spindle position, are coupled to a control system which controls the rotation of a socket in the arm which transfers tools between the tool storage drum and the tool transfer arm. The control system forces the socket in the arm to rotate in accordance with the difference between output signals of the synchro generators so that the key of the toolholder carried by the arm will, when transferred by tool transfer arm from the socket to the spindle, be aligned with the spindle key. The Sedgwick and Kato servo controlled spindle keylock apparatus are believed subject to the disadvantage that they result in increased machine complexity and cost.
In the past, mechanical clamping means have also been employed for stopping and locking the spindle of a machine tool in a predetermined angular orientation. Harman et al in U.S. Pat. No. 3,779,110 issued on Dec. 18, 1973 and Chabrier, in U.S. Pat. No. 3,683,490 issued on Aug. 15, 1972 describe a spindle keylock apparatus consisting essentially of a pin actuated by a piston for engaging a passage in a gear member or the like rotating co-jointly with the machine tool spindle. Although the Harman and Chabrier spindle locking apparatus are each operative to lock the spindle once the spindle reaches the predetermined angular orientation, neither device provides any means for sensing when the spindle reaches the predetermined angular orientation. Without such means, the Harman and Chabrier spindle lock devices may not always be operative to lock the spindle in the predetermined angular orientation.
To overcome the alleged disadvantage of the Chabrier and Harman apparatus, proximity switches have been employed to sense spindle position. Stephan et al in U.S. Pat. No. 3,709,623 issued on Jan. 9, 1973 describes a spindle keylock arrangement comprising a vee-shaped block attached to the spindle and a roller, the roller being urged by a solenoid, energized through a proximity switch, to engage the vee-shaped block to stop the spindle at the predetermined angular position. Another spindle keylock apparatus utilizing proximity switches is described in each of U.S. Pat. Nos. 3,994,061 and 4,019,246 issued to Tomita on Apr. 30, 1976 and Apr. 26, 1977, respectively, and U.S. Pat. No. 4,091,526 issued to Nakaso on Apr. 30, 1978. The spindle keylock apparatus described in each of the above-identified patents includes a pair of pivotally mounted claws which are urged by a solenoid or the like energized through a proximity switch to engage a dog that extends radially from the spindle. The above-described spindle keylock apparatus are each believed subject to the disadvantage that machine tool wear and vibration will likely cause proximity switch misalignment which may result in locking and stopping of the spindle at a position other than the predetermined angular position.
Other mechanical spindle keylocking apparatus includes the spindle keylock apparatus described by Antonietto et al in U.S. Pat. No. 3,604,803 issued on Sept. 14, 1971 and U.S. Pat. No. 3,691,899 issued on Sept. 19, 1972. The Antonietto spindle keylock apparatus comprises a double helical cam which is urged by an actuator against a cam follower carried by a sleeve keyed to a shaft coupled by a set of gears to the spindle. As the cam engages the cam follower, the sleeve, the shaft, and hence, the spindle, all rotate until the cam follower reaches the top of a cam, at which time the spindle will have reached its predetermined angular position. The Antonietto spindle locking apparatus is believed to suffer from the following disadvantage. Since the cam follower is carried on a sleeve keyed to a shaft coupled by gears to the spindle rather than being carried by the spindle itself, the spindle may not always be positioned in a precise angular orientation due to play between the cam follower and the spindle. Kato et al in U.S. Pat. No. 4,051,583 issued on Oct. 4, 1977 describes a spindle locking device apparatus which, like the Antonietto spindle lock apparatus operates on a shaft coupled by gears to the spindle rather than on the spindle itself and is thus believed to suffer from the same disadvantage as the Antonietto spindle lock apparatus.
Prior art spindle locking apparatus internal to the spindle for stopping and locking the spindle at a predetermined angular orientation without the need for proximity switches or servo controls are disclosed in U.S. Pat. No. 3,851,562 issued to Tomita on Dec. 3, 1974; U.S. Pat. No. 3,135,980 issued to Swanson et al on June 9, 1974 and U.S. Pat. No. 4,075,927 issued to Frazier on Feb. 28. 1978. While each of the internal spindle locking apparatus described in the above-identified patents overcomes many of the disadvantages attributable to other previously described spindle keylocks, the internally mounted spindle keylock apparatus are subject to the drawback that they may not be readily retrofitted to an existing spindle.
In contrast, the present invention concerns a spindle keylock apparatus for stopping and locking the spindle of a machine tool at precise angular orientation without the disadvantages and drawbacks attributable to other prior art devices.
It is an object of the present invention to provide a simple, inexpensive apparatus for stopping and locking the spindle or a machine tool at a predetermined angular orientation.
It is yet another object of the present invention to provide a spindle keylocking device for stopping and locking the spindle at a predetermined angular orientation which may be retrofitted to a pre-existing machine tool spindle.